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IEEE802.15.4 Informational Element encapsulation of 6tisch Join and Enrollment InformationUniversidad Diego PortalesEscuela de Informatica y Telecomunicaciones, Av. Ejercito 441Santiago, Region MetropolitanaChile+56 (2) 676-8121diego.dujovne@mail.udp.clSandelman Software Worksmcr+ietf@sandelman.caInternet
6lo Working GroupInternet-DraftIn TSCH mode of IEEE802.15.4, as described by ,
opportunities for broadcasts are limited to specific times and specific
channels. Nodes in a TSCH network typically frequently send Enhanced Beacon (EB)
frames to announce the presence of the network. This document provides a mechanism by which small
details critical for new nodes (pledges) and long sleeping nodes may be
carried within the Enhanced Beacon. describes the use of the time-slotted channel
hopping (TSCH) mode of . As further details in
, an Enhanced Beacon is transmitted during a slot
designated a broadcast slot.EDNOTE: Explain why broadcasts are rare, and why we need them. What the
Enhanced Beacon is, and what Information Elements are, and how the IETF has a
subtype for that area. Explain what kind of things could be placed in
Information Elements, how big they could be, and how they could be
compressed.In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
and indicate requirement levels for compliant STuPiD
implementations.As explained in section 6 of , the Enhanced Beacon
has a number of purposes: synchronization of ASN and Join Metric, timeslot
template identifier, the channel hopping sequence identifier, TSCH SlotFrame and
Link IE.The Enhanced Beacon (EB) is used by nodes already part of a TSCH network to
annouce its existance.
Receiving an EB allows a Joining Node (pledge) to learn about the network and
synchronize to it.
The EB may also be used as a means for a node already part of the network to
re-synchronize .There are a limited number of timeslots designated as a broadcast slot by each
router. These slots are rare, and with 10ms slots, with a slot-frame length of
100, there may be only 1 slot/s for the beacon.At layer 3, defines a mechanism by which nodes learn about
routers by listening for multicasted Router Advertisements (RA). If no RA is
heard within a set time, then a Router Solicitation (RS) may be multicast,
to which an RA will be received, usually unicast.Although reduces the amount of multicast necessary to do address
resolution via Neighbor Solicitation messages, it still requires multicast
of either RAs or RS. This is an expensive operation for two reasons: there
are few multicast timeslots for unsolicited RAs; if a pledge node does not
hear an RA, and decides to send a RS (consuming a broadcast aloha slot with
unencrypted traffic), unicast RS may be sent in response. XXXThis is a particularly acute issue for the join process for the following
reasons:use of a multicast slot by even a non-malicious unauthenticated node for
a Router Solicitation may overwhelm that time slot.it may require many seconds of on-time before a new pledge hears a Router
Soliciation that it can use.a new pledge may listen to many Enhanced Beacons before it can pick an
appropriate network and/or closest Join Assistant to attach to. If it must
listen for a RS as well as find the Enhanced Beacon, then the process may
take a very long time. creates a registry for new IETF IE subtypes.
This document allocates a new subtype TBD-XXX.This document documents a new IE subtype structure is as follows. As explained in
the length of the Sub-Type Content can be calculated from the
container, so no length information is necessary.
the proxy prority value contains a number from 0 to 0x7f. Lower numbers are considered
to be a higher preference. A priority of 0x7f indicates that the announcer should never
be considered as a viable enrollment proxy. Lower value indicates willing to act as a Join
Proxy as described in . Only unenrolled
pledges look at this value.
the pan priority is a value set by the DODAG root to indicate the relative
priority of this LLN compared to those with different PANIDs. This value may
be used as part of the enrollment priority, but typically is used by devices
which have already enrolled, and need to determine which PAN to pick.
Unenrolled pledges MAY consider this value when selecting a PAN to join.
Enrolled devices MAY consider this value when looking for an eligible parent device.
the rank "priority" is set by the 6LR which sent the beacon and is an
indication of how willing this 6LR is to serve as an RPL parent within a
particular network ID. This is a local value to be determined in other
work. It might be calculated from RPL rank, and it may include some
modifications based upon current number of children, or number of neighbor
cache entries available. This value MUST be ignored by pledges, it is for
enrolled devices only.
the Router Advertisement flag is set if the sending node will act as a
Router for host-only nodes that need addressing via unicast Router
Solicitation messages.
if the Proxy Address bit is set, then the lower 64-bits of the Join Proxy's
Link Layer address follows the network ID. If the Proxy Address bit is not set,
then the Link Layer address of the Join Proxy is identical to the Layer-2 8-byte
address used to originate this enhanced beacon.
In either case, the layer-2 address of any IPv6 traffic to the originator of
this beacon may use the layer-2 address which was used to originate the beacon.
if the P bit is set, then 64 bits (8 bytes) of address are present. The
Link Layer address of the Join Proxy is fe80 (as for any Link Layer address),
and the bits given in this field.
this is an variable length field, up to 16-bytes in size that uniquely identifies
this network, potentially among many networks that are operating in the same
frequencies in overlapping physical space. The length of this field can be
calculated as being whatever is left in the Information Element.In a 6tisch network, where RPL is used as the mesh routing protocol, the
network ID can be constructed from a SHA256 hash of the prefix (/64) of the
network. That is just a suggestion for a default value.
In some LLNs where multiple PANIDs may lead to the same management device
(the JRC), then a common value that is the same across all PANs MUST be configured.Here will be three examples of processing.All of the contents of this Information Element are sent in the clear. The
containing Enhanced Beacon is not encrypted.The Enhanced Beagon is authenticated at the layer-2 level using 802.15.4
mechanisms using the network-wide keying material. Nodes which are enrolled
will have the network-wide keying material and can validate the beacon.Pledges which have not yet enrolled are unable to authenticate the beacons.The use of a network ID may reveal information about the network. The use of
a SHA256 hash of the DODAGID, rather than using the DODAGID directly provides
some cover the addresses used within the network. The DODAGID is usually the
IPv6 address of the root of the RPL mesh.An interloper with a radio sniffer would be able to use the network ID to map
out the extend of the mesh network.Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID.
This entry should be called 6tisch-Join-Info.Thomas Watteyne provided extensive editorial comments on the document.
&RFC2119;
&RFC8137;
&RFC6775;
&RFC2461;
&RFC7554;
&I-D.ietf-6tisch-architecture;
&I-D.ietf-6tisch-minimal-security;
802.15.4-2015 - IEEE Standard for Low-Rate Wireless Personal Area Networks (WPANs)
&RFC8180;
&I-D.ietf-6tisch-dtsecurity-secure-join;
The rank priority was expanded to 2 bytes.00: The extension was originally for the use of Pledges only during the
enrollment/join process. Additional information was desired for nodes which
have already enrolled in order to aid in the joining (selecting of a parent)
of an RPL DAG. The term "join" was realized to be ambiguous, meaning
different things to different groups, and so the activity where the pledge
finds a "Join Proxy" has been named "enrollment"-1: This is an evolution of an earlier proposal which provided for storing an entire
IPv6 Router Adverisement in an Informational Element. It was deemed too general
a solution, possibly subject to mis-use. This proposal restricts the use to just
the key pieces of information required.